1. Field of the Invention
This invention relates to a metallized plastic molded product obtained by forming two protective films after base coat treatment and dry metallic film forming treatment and a method for producing same.
2. Description of the Prior Art
Hitherto, metallized plastic molded products comprising a plastic substrate which is subjected to a surface metallizing treatment have been used as various decorative articles, such as mirrors, and the like, utilizing the features of plastics such as high productivity, good moldability, light weight, and the like. Known metallizing methods include plating, hot-stamping, vacuum deposition, sputtering, ion plating, and the like. Especially, those which are produced by subjecting the surface of plastic substrates to chromium plating by a combination of chemical plating and electrical plating are widely used not only for interior decorative articles, but exterior automobile decorative articles. However, plating requires many and complicated steps and has problems in location of factories due to toxicity of plating solution and disposal of waste liquor and moreover it has the problem of high cost. On the other hand, the vacuum deposition method and the sputtering method are recognized as low cost and simple methods which have no waste liquor disposal problems.
The vacuum deposition method comprises subjecting the surface of a plastic substrate to a base coating treatment, a deposition treatment with metals such as aluminum, tin, and the like, in a high vacuum and then a top coating treatment, whereby a metallic appearance is imparted to the surface of the plastic molded product. The sputtering method comprises depositing atomic particles ejected from a target surface by sputtering on a substrate and requires a base coat layer and a top coat layer to obtain a beautiful appearance and high efficiency like the vacuum deposition method.
Plastic molded products on which aluminum is vacuum deposited are used as various interior decorative articles and those on which metals such as chromium, stainless steel and the like are vacuum deposited tend to be used as exterior automobile decorative articles in place of the products treated by plating methods. Furthermore, the sputtering method has also been examined to be used for the same purpose using stainless steel, chromium, and the like. However, exterior decorative parts to be substituted for those obtained by plating methods require high stain resistance, chemical resistance, solvent resistance, water resistance, corrosion resistance, wear resistance, heat resistance and weather resistance. Therefore, in the case of metallizing plastic molded products by vacuum deposition or the sputtering method, top coating materials which can provide said properties are required. Some thermosetting coating materials have such efficiency, but in view of the facts that the substrates are plastics low in heat resistance and that the coating materials must have strong adhesiveness to the metal layer, very few coating materials can be used. One example of such a material is two-pack urethane. In order to use a metallized plastic molded product having a protective coat of said urethane coating material as an exterior decorative article, a curing time of from 2 or 3 hours to one day is required at 70.degree.-80.degree. C. when the substrate is ABS resin. Nonetheless, cracks are apt to occur in the metal film layer to damage the appearance of the product. Thus, when thermosetting coating materials are used as protective coating materials for metallized plastic molded products treated by dry metal film forming methods such as vacuum deposition, sputtering and the like, there occur problems such as generation of cracks in the metal layer, long curing time, low productivity, high cost, and the like, and the thermosetting coating materials are not satisfactory as protective coating materials for exterior decorative metal film.
Ultraviolet curing coating materials which cure at ordinary temperatures in a short time overcome these defects of the thermosetting coating materials. Rapid curing at ordinary temperature is characteristic of ultraviolet curing coating materials, but they have a defect of low adhesiveness to metal due to their great volume shrinkage upon curing. Therefore, the conventional ultraviolet curing coating materials cannot be expected to provide a strong adhesiveness to a metal film layer. A need therefore continues to exist for ultraviolet curing coating materials having excellent adhesiveness to a metal film layer formed on a plastic molded product by dry type metal film forming methods such as vacuum deposition method or sputtering method and having excellent properties as coating materials for exterior decorative protective coating.